-LRB- CNN -RRB- `` It really depends what you want . Boy ? Girl ? Young ? Old ? ''

The man on the phone was offering us young children with the casualness of a market trader . After a week of back and forth phone calls , his initial caginess had given way to greed . He 'd heard my foreign accent and clearly decided I would pay more than the domestic rate .

`` We can get , '' he said .

We 'd been put in touch with the man through a contact on the ground . We were told he was one of the men running this `` unofficial '' displaced camp -- one of the many that has mushroomed in the town of Yola as the influx of people fleeing Boko Haram has grown beyond the capacity of the official camps .

It had all been heartbreakingly simple . We 'd asked who had children available to `` foster '' -- a catch-all code word designed to conceal the true intent of those offering up the orphaned children . The man on the phone was the end result of those inquiries .

When our colleague want to see them , he was shown a group of children and asked which one he wanted to take . One , two maybe ? He escaped by saying he needed to check with his `` madam '' -- me .

I called . The man picked up and began referring to me as `` sister . '' I told him we wanted to know what we 'd need to do , if we decided we did want to `` foster '' the children .

He told me , `` Sister , Jesus will reward me , '' so the `` fostering '' was free , he said . No need for any pesky paperwork -- just a reassurance from me that the children , if I chose to take them , would `` live in my heart . '' If I could also then find it `` in my heart '' to donate to those still in the camp , then that would be `` God 's work . ''

In spite of the harsh measures the Nigerian government has put in place to punish human traffickers , by the government 's own admission , 8 million children are currently engaged in forced labor .

The Global Slavery Index says Nigeria has the highest number of people in modern slavery of any sub-Saharan country . Paradoxically , the group also rates Nigeria 's anti-trafficking agency , Naptip , as one of the strongest government responses on the continent -- but it 's clearly overwhelmed by the realities of working in what is now a zone of military operations , Nigeria 's north . As the insecurity in the region has spiraled , the worry is that more and more children are falling through the cracks . And as Boko Haram increases its reliance on child suicide bombers , concerns are growing that orphaned children could end up in the hands of the terror group .

At the camp where we finally met the man face to face , there was no attempt at subterfuge . We spoke in normal tones in full view of the children playing . I could have had one of them , I was told , but because I 'd specified a younger child , they 'd only identified one so far -- a 3-year-old . Did I want to consider an older girl ? A 12-year-old maybe ? She could look after the 3-year-old , and cook and clean . Either way , two girls would be ready tomorrow , he said . I could see them then .

Our last phone conversation revolved around what an appropriate `` donation '' would be in exchange for the children . He could n't , he said , bargain for it . He then proceeded to do just that , laughing down the phone at my first tentative guess of $ 200 . Laughing again at $ 300 .

We finally found a figure he did n't find funny -- $ 500 . I put the phone down and we traveled back to the capital that day to show Naptip what we 'd found .

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CNN team finds a man at `` unofficial '' displaced camp willing to provide children to be `` fostered ''

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He says he ca n't take money for them , but eventually demands $ 500 for two girls